Unit 6.2 PLATELET STUDIES Flashcards
are produced from the cytoplasm of megakaryocytes
Platelets
Despite their tiny size, they are complex and metabolically active.
Platelets
They function in hemostasis by interacting with their environment to initiate and control hemostasis
Platelets
General characteristics of thrombocytes:
• Shape & origin:
• Diameter:
• Reference platelet count:
• Daily turnover:
• Lifespan:
• Function:
Thin disc cytoplasmic fragments
2 - 4 pm; Volume: 5 - 7 fL
150.000 - 450.000/uL
35 X 10%/L (+/- 4.3)
8 - 11 days
(Hemostasis) maintenance of vascular integrity and blood coagulation
bears the different glycoproteins
Glycocalyx
: Underlies the plasma membrane & receives message from the outside
Submembranous area
Peripheral zone:
Glycocalyx
Submembranous area:
Consists of a stable gel that regulates arrangement of internal organelles
Sol-Gel zone:
- provide the cytoskeleton
Microtubules & microfilaments
Where the alpha granules, dense bodies, mitochondria, lysosomes and peroxisomes are located.
Organelle zone:
2 membrane systems
Open canalicular system
Dense tubular system
- site of arachidonic acid synthesis and functions as a calcium sequestering pump
Dense tubular system
delivery routes
Open canalicular system
High Molecular Weight Kininogen Fibrinogen;
Promote coagulation
Factor V
Promote coagulation
von Willebrand Factor
Promote coagulation
Alpha granules
Promote coagulation
ADP;
Promote aggregation
Calcium
Promote aggregation
Platelet factor 4
Promote aggregation
Thrombospondin
Promote aggregation
Dense bodies
Promote aggregation
Alpha granules
Promote coagulation
Promote aggregation
Promote vasoconstriction
Promote vascular repair
Other system affected
Serotonin
Promote vasoconstriction
Thromboxane A2 precursors
Promote vasoconstriction
Dense bodies
Promote vasoconstriction
Membrane phospholipids
Promote vasoconstriction
Platelet derived growth factor
Promote vascular repair
Beta thromboglobulin
Promote vascular repair
Plasminogen
Other system affected
Alpha 2-antiplasmin
Other system affected
C1 esterase inhibitor
Other system affected
Ability of platelets to attach to non-platelet surface. This allows platelets to adhere to damaged endothelium.
Adhesion
Requires plasma von Willebrand Factor and Gp Ib-IX
Adhesion
Alpha & dense granules release substances that will contribute to platelet aggregation and activation of the coagulation system
Platelet Release Reaction
Platelets stick to one another to form an initial platelet plug.
Platelet aggregation
Induced by stimuli such as ADP, thrombin, TxA2, collagen & epinephrine.
Platelet aggregation
Requires Gp IIb-IIIa and plasma fibrinogen.
Platelet aggregation
Deficiency/Defect in Gp Ib-IX
Bernard-Soulier:
Characterized by large platelets, thrombocytopenioa, prolonged and Bleeding Time.
Bernard-Soulier:
Platelets show normal aggregation with epinephrine, ADP and collagen but not with ristocetin.
Bernard-Soulier:
Aggregation test: same with Bernard-Soulier
von Willebrands disease
Deficiency/Defect in Gp IIb-IIIa
Glanzmann’s Thrombasthenia
Platelets show normal aggregation with ristocetin but not with epinephrine, ADP nor collagen.
Glanzmann’s Thrombasthenia
- Decreased production
Thrombocytopenia:
- Dilutional (e.g. following blood transfusion)
Thrombocytopenia:
- Increased destruction (immune and non-immune causes)
Thrombocytopenia:
- Splenic sequestration
Thrombocytopenia:
- Myeloproliferative (uncontrolled production by the bone marrow)
Thrombocytosis:
- Reactive thrombocytosis (in response to hemolytic anemias)
Thrombocytosis:
